Typically in high flow gain single-stage jet pipe servovalves, both the pressure gain and flow gain rise rather sharply upon the application of appropriate electrical signals to the torque motor causing movement of the ejector jet relative to the receptors in the servovalve. Traditionally, both pressure and flow gain track each other closely. It has been found that in some applications, rapid rises in pressure, that is steep pressure gain, may generate unwanted signals. For example, in redundant control systems such rapid rises in pressure may appear to detection portions of the system as a failure or malfunction in one or more portions of the system. It has thus been determined that in some applications, single stage jet pipe servovalves or the first stage of multi-stage valves, it is desireable to compensate such pressure gain by reducing the level thereof without at the same time degrading the flow gain characteristics of the valve.
The present invention provides differential pressure gain compensation for single stage jet pipe servovalves or in the first stage of multiple stage jet pipe servovalves so as to maintain a relatively low level of pressure gain without degrading the flow gain thereof. Such is accomplished by providing a mechanical feedback source which is proportional to the pressure differential between the receptors of the jet pipe servovalve.
Pressure feedback in electrohydraulic servovalves is well known in the prior art and the best known such prior art is reflected in U.S. Pat. Nos. 3,398,647 and 3,487,750. The devices disclosed in each of these two prior art patents generate a mechanical feedback signal responsive to load pressure at the utilizing apparatus. The mechanical feedback signal is then applied to the servo control system. Although these prior art devices develop mechanical feedback signals responsive to pressure at the load, applicants are unaware of any prior art devices which utilize a mechanical feedback signal proportional to pressure differential at the receptors for purposes of compensating pressure gain.